Evidence for metallic states in potassium-intercalated picene film on graphite

We report the results of photoemission spectroscopy on the potassium concentration (x) dependence of K_x picene films on graphite. The results show a systematic shift of a whole valence band and the appearance of a clear Fermi edge for a certain value of x, with additional structures at higher binding energies. Observed spectral evolutions are reminiscent to those of doped C₆₀, implying that the K_x picene film has multiple phases depending on the K concentration. Appearance of a clear Fermi edge, in contrast to multilayer K_x picene films on Au, SiO₂, and Ag(111) substrates, where no clear Fermi edges are observed, suggests that the emergence of the metallic states for K_x picene films depends on the specific molecular orientations in the films on different substrates.